1. Field of the Invention
The present invention relates to a fire detector and a fire receiver which are equipped with a self-monitoring function.
2. Description of the Related Art
A conventional fire detector, e.g. a photoelectric type fire detector, is provided with a light emitting element and a light receiving element in a black box. In such a photoelectric type fire detector, the light emitted by the light emitting element is scattered by smoke, the scattered light is detected by the light receiving element, the detection signal is amplified through an amplifier, and the smoke concentration is determined according to the level of the output of the amplifier, thereby carrying out fire monitoring. In addition to such fire monitoring, the photoelectric type fire detector also detects the steady-state value (the steady-state value issued by the amplifier in the absence of a fire) of the photoelectric fire detector so as to carry out steady-state value monitoring, whereby it checks the photoelectric type fire detector for a malfunction according to the detected steady-state value.
A conventional system for checking the photoelectric type fire detector for a failure has been disclosed in Japanese Patent Publication No. 64-4239. The conventional system is provided with a light emitting element and a light receiving element for receiving the light from the light emitting element, and is also provided with an upper limit comparing circuit and a lower limit comparing circuit for comparing an output signal of the light receiving element. Remote control is carried out through the receiver to control the two comparing circuits incorporated in the photoelectric fire detector.
The conventional system has such a shortcoming that the steady-state value monitoring operation cannot be performed until the comparing circuits in the photoelectric fire detector are controlled through the receiver. Hence, the photoelectric fire detector cannot detect its own malfunction by itself, causing a heavy burden on the receiver.